Transistor fabrication methods using reduced width sidewall spacers

ABSTRACT

Transistor fabrication methods ( 50 ) are presented in which shrinkable sidewall spacers ( 120 ) are formed ( 66, 68 ) along sides of a transistor gate ( 114 ), and a source/drain implant is performed ( 74 ) after forming the sidewall spacer ( 120 ). The sidewall spacer width is then reduced by annealing the shrinkable sidewall spacer material ( 76 ) following the source/drain implant ( 74 ).

FIELD OF INVENTION

The present invention relates generally to semiconductor devices and methods for making the same.

BACKGROUND OF THE INVENTION

Current trends in the semiconductor industry include faster switching speeds, reduced power consumption, and lower operating voltages, wherein the performance of MOS transistors needs to be correspondingly improved. For example, high-speed transistors are required for modern wireless communications systems, portable computers, and other low-power, low-voltage devices, wherein MOS transistors must be adapted to operate at lower voltages using less power. Carrier mobility in a MOS transistor has a significant impact on power consumption and switching performance. The carrier mobility is a measure of the average speed of a carrier (e.g., holes or electrons) in a given semiconductor, given by the average drift velocity of the carrier per unit electric field. Improving the carrier mobility in the channel region of a MOS transistor can improve the switching speed, and can also facilitate operation at lower voltages, alone or in combination with reducing the transistor channel length and gate dielectric thickness to improve current drive and switching performance.

Carrier mobility of a MOS transistor is affected by the mechanical stress in the device channel. The carrier mobility can be improved by depositing silicon/germanium alloy or other material layers between upper and lower silicon layers under compressive stress, in order to enhance hole carrier mobility in a channel region. For NMOS transistors, tensile stress in the channel material improves carrier mobility by lifting conduction band degeneracy. However, buried silicon/germanium channel layer devices have shortcomings, including increased alloy scattering in the channel region that degrades electron mobility, a lack of favorable conduction band offset which mitigates the enhancement of electron mobility, and the need for large germanium concentrations to produce strain and thus enhanced mobility. Furthermore, such additional alloy layers and silicon layers are costly, adding further processing steps to the device manufacturing procedure.

Thus, there is a need for methods and apparatus by which the carrier mobility and other electrical operational properties of MOS transistor devices may be improved so as to facilitate improved switching speed and low-power, low-voltage operation, without significantly adding to the cost or complexity of the manufacturing process.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

The invention relates to methods for transistor fabrication, in which relatively wide sidewall spacers are provided along lateral sides of a transistor gate structure during deep source/drain implantation to control the location of the source/drains on either side of the transistor channel region, and the spacers are narrowed after the deep source/drain implant to facilitate the inducing enhanced stress in the transistor channel, to improve source/drain contact resistance, and to improve PMD gap fill. The invention may be employed in conjunction with stress inducing PMD liner material layers formed over the transistor after source/drain implantation, wherein the reduced sidewall spacer width facilitates inducing enhanced stress at the center of the transistor channel.

In accordance with one aspect of the invention, a method is provided for fabricating a transistor, comprising forming a sidewall spacer along a side of a gate structure, implanting dopants into a source/drain region of a semiconductor body after forming the sidewall spacer, and reducing the sidewall spacer width after implanting the dopants. The spacer may be formed using a material that shrinks upon application of energy during processing following the source/drain implantation. In one implementation, a shrinkable sidewall spacer material is formed over the gate structure and over the source/drain region, and an etch process is performed, leaving a shrinkable sidewall spacer along the lateral side of the gate structure over a portion of the source/drain region. The spacer material may be thermally shrinkable silicon oxide, nitride, oxynitride, carbide, or Si_(W)O_(X)C_(Y)N_(Z) with a non-zero hydrogen content, which can be deposited using low temperature chemical vapor deposition (CVD) processes, where the spacer is then shrunk or reduced by annealing after the source/drain implantation. A stress inducing material may then be formed over the transistor, wherein the reduced sidewall spacer width facilitates lower source/drain contact resistance and/or improved channel carrier mobility through induced stress in the semiconductor body.

The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified flow diagram illustrating an exemplary transistor fabrication method in accordance with the present invention;

FIG. 2 is a detailed flow diagram illustrating an exemplary implementation of the invention using dual sidewall spacers; and

FIGS. 3A–3L are partial side elevation views in section illustrating an exemplary integrated circuit with MOS transistors undergoing fabrication processing generally in accordance with the method of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

One or more implementations of the present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures are not necessarily drawn to scale.

The invention provides techniques for improving transistor performance by facilitating application of stress to improve carrier mobility, such as tensile stress provided to NMOS channel regions, and by source/drain contact resistance improvement. In one particular implementation illustrated and described hereinafter, a stress inducing PMD liner nitride film is formed over the transistor following silicide processing to impart stress in the transistors, where the liner protects the underlying transistors from a subsequently formed pre-metal dielectric (PMD) material and operates as an etch-stop layer in forming openings for contacts to transistor terminals through the PMD material. In accordance with the invention, a shrinkable sidewall spacer technique is employed to provide wide spacers during deep source/drain implantation, with a narrower (e.g., reduced width) spacer during silicide processing and PMD liner formation, by which the contact resistance of the silicide source/drain contact can be reduced, PMD gap fill can be improved, and by which the PMD liner has a greater impact on the stress level at the center of the transistor channel.

The inventors have appreciated that it is desirable to increase carrier mobility throughout the length of the transistor channel, including the central portion of the channel, which may be accomplished by depositing certain stress inducing materials over the transistors. However, the inventors have found that the induced stress at any location in the semiconductor material varies with the distance between the stress inducing material and the semiconductor material. In the case where a PMD liner material is deposited over the transistor after silicide processing, the resulting stress at the central portion of the channel can be increased by reducing the distance from the PMD liner to the channel center. The invention provides techniques for reducing this distance, and hence increasing the stress effect at the channel center, by reducing the sidewall spacer width at the point where the PMD liner is formed during fabrication.

The improved induced stress, in turn, results in improved carrier mobility and hence improved transistor drive current. In one example, reducing the sidewall spacer width from 700 Å to 500 Å results in about 20–25% increase in carrier mobility, leading to about 5–10% higher drive current. However, the inventors have further appreciated that merely decreasing the sidewall spacer width throughout fabrication processing may lead to unacceptable transistor leakage current because the sidewall spacer width also serves to set the lateral location of the deep source/drain dopants during implantation. Thus, if the sidewall spacers are too narrow during deep source/drain implantation, the dopants may diffuse too far under the gate (e.g., toward the center of the channel) during subsequent processing, which may cause higher transistor leakage current.

Referring initially to FIG. 1, the invention accordingly provides fabrication methods in which initially wide sidewall spacers are provided during deep source/drain implantation, and the spacers are then narrowed prior to forming the stress inducing PMD liner, whereby improved transistor performance can be realized without adversely impacting leakage current. A method 2 is illustrated in FIG. 1 in accordance with the present invention. While the method 2 and other methods are illustrated and described below as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the devices and systems illustrated and described herein as well as in association with other structures not illustrated.

Beginning at 4, isolation processing and well formation are performed at 6 in the method 2, wherein any suitable isolation processing may be performed at 6, such as local oxidation of silicon (LOCOS) processing to form field oxide (FOX) isolation structures, shallow trench isolation (STI) processing, or other suitable techniques to form isolation structures between active regions of a semiconductor body. Patterned gate structures are then formed at 8 over channel regions of the semiconductor body. The invention may be employed in fabricating transistors with any suitable gate structure, such as a thin gate dielectric (e.g., oxides such as SiO₂, or other dielectric material) formed over the semiconductor channel, with an overlying conductive gate (e.g., doped polysilicon, metal, or stacks or multi-layer gate contact structures), which are formed at 8 by any suitable means, such as deposition of the gate dielectric and gate contact layers, followed by etching to define the patterned gate structure. At 10, a drain extension implant is performed to initially dope a shallow portion of prospective source/drain regions on either side of the channel. Any suitable drain extension implant may be performed at 10, including but not limited to lightly-doped-drain (LDD) implants, moderately-doped-drain (MDD) implants, etc.

Shrinkable sidewall spacers are formed at 12 along lateral sides of the patterned gate structures. As described further below with respect to FIGS. 2 and 3A–3L, the sidewall spacers may be formed at 12 of high shrinkage material using low temperature deposition techniques, thereby providing shrinkable sidewall spacers that may be controllably reduced in size (e.g., narrowed) upon application of thermal or other types of energy. Deep source/drain implantation is performed at 14 to further define the source/drain regions with the spacers in place, after which the width of the sidewall spacers is reduced at 16, such as during source/drain implant activation annealing. Silicide is then formed at 18 over the source/drains and the gate contact, and a PMD liner is formed at 20 to impart stress in the transistor for carrier mobility improvement. A PMD dielectric material layer is then formed over the liner at 22 and conductive contacts are formed at 24 through select portions of the PMD layer to provide electrical connection to the transistor gate and source/drains. Interconnect metallization and other back end processing is then performed at 26 to complete the device, and the method 2 ends at 28.

Referring now to FIGS. 2 and 3A–3L, FIG. 2 illustrates an exemplary detailed method 50 in accordance with the invention where shrinkable sidewall spacers are employed to provide relatively wide spacers during deep source/drain implantation (e.g., to control the lateral location of the source/drains and hence to control transistor leakage current) and to subsequently provide narrowed spacers during silicidation and PMD liner formation (e.g., to improve contact resistance, PMD gap fill, and carrier mobility). FIGS. 3A–3L illustrate an exemplary integrated circuit device 102 with MOS transistors undergoing fabrication processing generally in accordance with the method 50 of FIG. 2.

Beginning at 52 in FIG. 2, isolation processing and well formation are performed at 54. In FIG. 3A, the exemplary device 102 is illustrated following well formation and isolation processing beginning with a semiconductor body 104. The device 102 comprises includes NMOS and PMOS active regions of the semiconductor body 104, wherein a p-well 106 is formed in the NMOS region and an n-well 108 is formed in the PMOS region. STI isolation structures 110 are formed by etching trenches in isolation regions of the semiconductor body 104 and filling the trenches with oxide or other insulating material to separate the active regions and the devices thereof from one another and from other electrical components and circuits in the device 102, although LOCOS type field oxide isolation structures may alternatively be used.

At 56 in FIG. 2, patterned gate structures are formed over prospective channel regions of the semiconductor body 104. As illustrated in FIG. 3A, the exemplary gate structures in the NMOS and PMOS regions include a thin gate dielectric 112 (e.g., SiO₂, etc.) and a conductive gate contact 114 (e.g., doped polysilicon or other conductive material), wherein the gate dielectric 112 is situated between the conductive gate contact 114 and the prospective transistor channel regions. Any suitable gate structures may be employed within the scope of the invention, including but not limited to the illustrated gate dielectric and contact structures 112, and 114, respectively, or other suitable material layers or multi-layers, including but not limited to metal gate layers. In the exemplary implementation, the gate dielectric material 112 is formed over the surface of the semiconductor body 104 by thermal oxidation and/or deposition, after which a layer of polysilicon 114 is deposited over the gate dielectric layer 112. The polysilicon 114 is then selectively etched using reactive ion etching or other suitable etch process with corresponding etch masking to define the patterned gate structures as shown in FIG. 3A in the NMOS and PMOS regions of the device 102.

The method 50 continues at 58 in FIG. 2, where a polysilicon oxide layer is formed through thermal oxidation or suitable deposition process (e.g., chemical vapor deposition (CVD)). Thereafter, thin nitride offset spacers are formed at 60. FIG. 3B illustrates the prospective NMOS region of the device 102 with thin poly oxide structures 115 formed along the sides of the patterned gate 112, 114, and nitride offset spacers 117 formed along the outer sides of the poly oxide 115. Although the remaining description below is provided in the context of fabricating an NMOS transistor, similar processing steps can be employed at suitable points in the process flow to construct PMOS transistors, with n-type regions being generally substituted for p-type regions and vice versa. A drain extension (e.g., LDD) implant is then performed at 62 in FIG. 2. As illustrated in FIG. 3C, a low energy, high dose LDD implantation process 200 is performed to provide n-type dopants into shallow portions of the exposed prospective source/drain regions 116 within the p-well 106. After the LDD implant at 62, the method 50 proceeds to 64 where a cap oxide 119 is formed over the device 102, as illustrated in FIG. 3D.

In accordance with the present invention, shrinkable sidewall spacers are then formed at 66–68 in FIG. 2. Shrinkable sidewall spacers are any sidewall spacers that can be narrowed (e.g., the width can be reduced) in a controlled fashion by subsequent application of energy, so as to provide a first width during source/drain implantation and a narrower (e.g., smaller) width during subsequent silicidation and/or during formation of an overlying stress inducing material. In this regard, the sidewall spacers of the invention may be reduced through application of thermal energy (e.g., activated by annealing), or alternatively may be reduced by light activated or chemically activated, wherein application of energy causes the material to shrink.

In FIG. 2, a high shrinkage sidewall spacer material 120 is deposited or otherwise formed at 66 over the gate structure 112, 114 and over the source/drain regions 116 via a chemical vapor deposition (CVD) process 202, as illustrated in FIG. 3E. At 68, an anisotropic sidewall spacer etch process 204 is performed (FIG. 3F) to selectively remove the first sidewall spacer material 120 from over the gate 114 and an outer portion of the source/drain regions 116, leaving shrinkable sidewall spacers 120 situated along the lateral sides of the gate structure (e.g., outward of the poly oxide 115 and the nitride offset spacers 117 in this example). Any etch process 204 can be employed which operates to remove the first spacer material 120 in a generally anisotropic fashion, leaving the sidewall spacers 120 having a first width W1 as illustrated in FIG. 3F.

Any suitable materials, thickness, and deposition techniques may be employed to form the spacer material 120 at 66 within the scope of the invention. In the illustrated implementation, the sidewall spacer material 120 is thermally shrinkable silicon oxide (Si_(W)O_(X)), silicon nitride (Si_(W)N_(X)), silicon oxynitride (Si_(W)O_(X)N_(Y)), silicon carbide (Si_(W)C_(X)), or Si_(W)O_(X)C_(Y)N_(Z) having a non-zero hydrogen content. In one example, the material 120 is deposited at 66 using a plasma enhanced chemical vapor deposition (PECVD) process 202 at a deposition temperature of about 350 degrees C. or less, preferably about 300 degrees C. or less. In another example, a sub-atmospheric chemical vapor deposition (SACVD) process 202 is employed at 66 to form high shrinkage silicon oxide 120. In the illustrated device, moreover, the deposited high shrinkage spacer material 120 comprises hydrogen, although this is not a strict requirement of the invention. The inventors have appreciated that such high shrinkage materials can be deposited at low temperatures and then subsequently shrunk or reduced by annealing after the source/drain implantation. In the exemplary device 102, the initial spacer width W1 in FIG. 3F is about 800 Å, wherein subsequent annealing at about 1050 degrees C. or more after source/drain implantation (e.g., at 76 in FIG. 2 below) results in a shrinkage of about 20% (e.g., to a final width of about 600 Å in this example).

At 70 in FIG. 2, any remaining cap oxide (e.g., formed at 64 above) is removed via a wet or dry etch process 210, as illustrated in FIG. 3G, and an etch clean operation is performed at 72. In one example, a wet chemistry is used at 72, that is preferably optimized according to the sidewall spacer material 120 so as to minimize sidewall spacer loss during the wet clean operation at 72. Referring also to FIG. 3H, a deep source/drain implantation process 214 is performed at 74 to further dope the source/drain regions 116 with n-type dopants with the sidewall spacers 120 in place, where the lateral extent or location of the implanted deep source/drain dopants is largely determined by the initial (e.g., as-deposited) width W1 of the sidewall spacers 120. The deep source/drain implantation at 74 is distinguished from the earlier drain extension implant (e.g., the LDD implant at 62 above) and occurs after sidewall spacer formation. The resist for source/drain patterning is then removed.

Referring also to FIG. 31, a source/drain activation anneal process 216 is performed at 76, which may be performed at any suitable temperature for any suitable duration that provides source/drain dopant activation and the desired spatial diffusion thereof. In addition, the activation anneal process 216 concurrently reduces the width of the shrinkable sidewall spacers 120 to a second width W2, such as about 600 Å or less (e.g., a width reduction of about 20% or more) in the illustrated device 102. In this example, the activation anneal process 216 is performed at a temperature of about 1050 degrees C. or more for a few seconds (e.g., a spike anneal), although any suitable time and temperature settings may be employed to shrink temperature activated shrinkable sidewall spacer materials within the scope of the invention. Furthermore, while the exemplary implementation advantageously employs the pre-existing source/drain activation anneal process step to concurrently provide dopant activation and sidewall spacer width reduction, a separate process step may alternatively be performed for spacer width reduction, including application of other energy types for light activated or chemically activated shrinkable sidewall spacer materials, wherein all such variant implementations are contemplated as falling within the scope of the present invention and the appended claims.

The reduction in the sidewall spacer width after deep source/drain implantation (e.g., to the narrower width W2 in FIG. 31) provides several advantages. First, as discussed above, it is desirable to have relatively wide spacers 120 (e.g., W1 in FIG. 3H) to control the lateral location of the deep source/drain regions 116 during the implantation at 74, and in addition, it is desirable to have narrower spacers 120 when siliciding the source/drains 116 (e.g., W2 in FIG. 31 and thereafter). The narrowed spacers 120 result in wider silicided source/drain contacts, thereby reducing the source/drain contact resistance of the transistor. Furthermore, narrower spacers 120 facilitate application of higher stresses in the channel region of the semiconductor body 104 under the gate dielectric 112 when a stress inducing material is deposited over the transistors following silicidation.

In addition, where the high shrinkage spacer material 120 includes hydrogen, hydrogen is released during the source/drain activation anneal at 76, and may operate to facilitate dopant diffusion to reduce the impurities in the channel region. In NMOS transistors, for example, the source/drains are typically doped or implanted with Arsenic or other n-type dopants in the LDD implant (e.g., at 62 in FIG. 2), wherein pocket or halo type implants are often employed using Boron or other p-type dopants at the corners of the channel region. The inventors have appreciated that Boron diffusion from such pocket implants tends to pile up at the interface between the channel region of the semiconductor body 104 (e.g., typically silicon) and the overlying gate dielectric (e.g., oxide). While not wishing to be tied to any particular theory, it is believed that where the sidewall spacers 120 release hydrogen during annealing, some of the released hydrogen moves goes downward and promotes diffusion of the Boron toward the sidewall spacers 120 and toward the cap oxide 119, rather than toward the channel. Thus, the high shrinkage sidewall spacers 120 may facilitate reduction in the amount of dopant impurities in the channel, and help to produce a so-called retrograde channel profile.

Referring now to FIG. 3J, after the sidewall spacer widths have been reduced, silicide processing is performed at 78 in FIG. 2, to create conductive silicide structures 124 at the upper surfaces of the transistor gate 114 and the source/drains 116. Any suitable silicide materials 124 may be employed, such as nickel or cobalt silicide. In one example, a layer of nickel is deposited over the device 102 after reducing the width of the sidewall spacers 120, wherein the deposited nickel overlies the gate polysilicon 114 of the patterned gate structure and also overlies the doped source/drains 116 of the substrate 104. A thermal anneal is performed to react the nickel with the gate polysilicon 114 and with the source/drain substrate material 116, thereby forming a metal silicide 124 above the transistor terminals 114 and 116, as illustrated in FIG. 3J. It is noted at this point that the reduction of the sidewall spacer widths allows source/drain silicide formation closer to the gate 114, whereby the source/drain silicide 124 will have improved (e.g., lower) contact resistance.

As a further benefit, the narrowed spacers 120 allow formation of a stress inducing material layer closer to the center of the channel region below the gate dielectric 112. Furthermore, the shrinkage of the spacer material 120 itself may induce some stress in the transistor channel even before the formation of the stress inducing liner material. As illustrated in FIG. 3K, a PECVD process 218 is performed at 80 to deposit a silicon nitride PMD liner 130 over the gate 114 and the sidewall spacers 120, wherein the liner 130 can be any material that provides a stress in the transistor. In the exemplary device 102, the silicon nitride PMD liner 130 has an as-deposited hydrogen content of about 20 atomic percent or more and provides an initial tensile stress of about 400–600 MPa in at least a portion of the NMOS region of the semiconductor body 104. Any suitable nitride deposition process 218 may be used, wherein the exemplary PECVD process 218 is performed at about 350 degrees C. or less, with a deposition chamber pressure of about 3.5 Torr or more, a silane (SiH₄) gas flow of about 150 sccm or less, and an ammonia (NH₃) gas flow of about 2500–3000 sccm, using high frequency RF power of about 50 W at 13.56 MHz, and low frequency power of about 10–20 W at 350 KHz.

The exemplary liner film 130 is meta-stable with a relatively high hydrogen content and operates to impart a moderate tensile stress in all or a portion of the NMOS region of the substrate 104 after the deposition process 218, such that subsequent application of thermal energy during subsequent back-end processing causes a reduction in the hydrogen content and an increase in the applied tensile stress in the NMOS region (e.g., to about 1 GPa or more in at least a portion of the NMOS region). Moreover, the PMD liner 130 may be formed to any suitable thickness within the scope of the invention, such as about 300 Å or more, about 500 Å in one example, where the liner 130 also operates as an etch stop layer in the creation of contact openings in a subsequently formed PMD dielectric material, wherein the thickness of the layer 130 may be selected according to the etch stop performance as well as according to the induced stress considerations.

In FIG. 3L, an initial dielectric (PMD) layer 132 is then deposited (e.g., at 82 in FIG. 2) over the nitride liner 130, where any suitable PMD materials and thicknesses may be employed. In one example, the PMD layer 132 comprises a phosphorous doped silicon oxide, deposited to a thickness of about 9000 Å over the stress inducing PMD liner 130, where the PMD layer 132 provides insulation between overlying and underlying conductive features, such as between the silicide contacts 124 and later-formed conductive interconnect features in subsequent metalization layers of the device 102 (not shown). The deposition of the PMD layer 132 and subsequent back-end processing steps provide thermal processing of the PMD liner nitride 130, causing the as-deposited meta-stable nitride material layer 130 to further stabilize and thereby to increase the tensile stress provided in the semiconductor body 104, wherein the proximity of the liner 130 to the transistor channel and the resulting stress related mobility improvements are enhanced by the selective reduction of the sidewall spacer widths. Conductive contacts 134 are then formed at 84 through the PMD layer 132 to connect with the silicide 124, after which a multilayer or multi-level interconnect routing (e.g., metalization) structure (not shown) is then formed above the PMD layer 132, and other back-end processing is performed at 86 before the method 50 ends at 88.

Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. 

1. A method of fabricating a transistor, the method comprising: forming a gate structure over a channel region of a semiconductor body; forming a sidewall spacer along a lateral side of the gate structure; performing a deep source/drain implant to implant dopants into a source/drain region of the semiconductor body after forming the sidewall spacer; and reducing a width of the sidewall spacer after the deep source/drain implant.
 2. The method of claim 1, wherein forming the sidewall spacer comprises: forming a shrinkable sidewall spacer material over the gate structure and over the source/drain region of the semiconductor body; and performing an anisotropic etch process to selectively remove the shrinkable sidewall spacer material from over the gate structure and from an outer portion of the source/drain region, leaving the sidewall spacer along the lateral side of the gate structure over a portion of the source/drain region.
 3. The method of claim 2, wherein forming the shrinkable sidewall spacer material comprises depositing at least one of Si_(W)O_(X), Si_(W)O_(X)N_(Y), Si_(W)N_(X), Si_(W)C_(X), and Si_(W)O_(X)C_(Y)N_(Z) z over the gate structure and over the source/drain region of the semiconductor body.
 4. The method of claim 3, wherein the shrinkable sidewall spacer material is deposited using a plasma enhanced chemical vapor deposition process at a deposition temperature of about 350 degrees C. or less.
 5. The method of claim 2, wherein forming the shrinkable sidewall spacer material comprises depositing ozonated Si_(W)O_(X) using a sub-atmospheric chemical vapor deposition process.
 6. The method of claim 2, wherein reducing the width of the sidewall spacer comprises reducing the width of the sidewall spacer by about 20 percent or more after the deep source/drain implant.
 7. The method of claim 6, wherein reducing the width of the sidewall spacer comprises heating the sidewall spacer after the deep source/drain implant.
 8. The method of claim 6, wherein reducing the width of the sidewall spacer comprises heating the sidewall spacer to about 1050 degrees C. or more after the deep source/drain implant.
 9. The method of claim 2, wherein the shrinkable sidewall spacer material comprises at least one of Si_(W)O_(X), Si_(W)O_(X)N_(Y), Si_(W)N_(X), Si_(W)C_(X), and Si_(W)O_(X)C_(Y)N_(Z) having a non-zero hydrogen content.
 10. The method of claim 2, wherein reducing the width of the sidewall spacer comprises heating the sidewall spacer after the deep source/drain implant.
 11. The method of claim 1, wherein reducing the width of the sidewall spacer comprises reducing the width of the sidewall spacer by about 20 percent or more after the deep source/drain implant.
 12. The method of claim 11, wherein reducing the width of the sidewall spacer comprises heating the sidewall spacer after the deep source/drain implant.
 13. The method of claim 1, wherein reducing the width of the sidewall spacer comprises heating the sidewall spacer after the deep source/drain implant.
 14. The method of claim 1, wherein the shrinkable sidewall spacer material comprises at least one of Si_(W)O_(X), Si_(W)O_(X)N_(Y), Si_(W)N_(X), Si_(W)C_(X), and Si_(W)O_(X)C_(Y)N_(Z).
 15. The method of claim 14, wherein the shrinkable sidewall spacer material comprises hydrogen.
 16. The method of claim 1, wherein the sidewall spacer is formed at a temperature of about 350 degrees C. or less.
 17. The method of claim 1, further comprising forming a stress inducing material over the gate and the sidewall spacer after reducing the width of the sidewall spacer.
 18. A method of fabricating a transistor, the method comprising: forming a shrinkable sidewall spacer along a side of a gate structure; implanting dopants into a source/drain region of a semiconductor body after forming the sidewall spacer; and reducing a width of the sidewall spacer after implanting the dopants.
 19. The method of claim 18, wherein forming the shrinkable sidewall spacer comprises: forming a shrinkable sidewall spacer material over the gate structure and over the source/drain region; and performing an anisotropic etch process to selectively remove the shrinkable sidewall spacer material from over the gate structure and from an outer portion of the source/drain region, leaving the shrinkable sidewall spacer along the lateral side of the gate structure over a portion of the source/drain region.
 20. The method of claim 19, wherein the shrinkable sidewall spacer material is formed using a chemical vapor deposition process at a deposition temperature of about 350 degrees C. or less.
 21. The method of claim 18, wherein the shrinkable sidewall spacer comprises at least one of Si_(W)O_(X), Si_(W)O_(X)N_(Y), Si_(W)N_(X), Si_(W)C_(X), and Si_(W)O_(X)C_(Y)N_(Z).
 22. The method of claim 21, wherein the shrinkable sidewall spacer comprises hydrogen.
 23. The method of claim 18, wherein the shrinkable sidewall spacer is formed at a temperature of about 350 degrees C. or less.
 24. The method of claim 18, further comprising forming a stress inducing material over the gate and over the sidewall spacer after reducing the width of the sidewall spacer. 